VB.NET - StringBuilder Examples

Append example. We see a program that declares a new StringBuilder. Then it uses a simple For-loop and appends integers and 1-character strings to it.

For

Info The first directive "Imports System.Text" lets us reference StringBuilder more directly in the program.

Imports

StringBuilder Append

Imports System.Text Module Module1 Sub Main() ' Create StringBuilder and append to it in a loop. Dim builder As New StringBuilder() For i As Integer = 0 To 2 builder.Append(i).Append(" ") Next Console.WriteLine(builder) End Sub End Module

0 1 2

AppendFormat. Next we use AppendFormat. This function receives a format string, usually with substitutions such as {0}, and parameters to fill those substitutions.

Detail Using format strings, as with AppendFormat, often yields code that is easier to read and understand.

Imports System.Text Module Module1 Sub Main() ' StringBuilder declaration. Dim builder As New StringBuilder Dim number As Integer = 1 builder.AppendFormat("R: {0} ({1}).", "ABC", number) ' Print the resulting string data. Console.WriteLine(builder) End Sub End Module

R: ABC (1).

Replace. This example creates a StringBuilder with the constructor. Then it calls Replace() to replace one substring with another. Performance is good. No string temporaries are created.

Here The starting buffer for the StringBuilder has the word "the" in it. After the Replace method is run, it instead has the word "my."

Return Replace() returns a reference to the StringBuilder. We can ignore this return value, or call another method on it.

Imports System.Text Module Module1 Sub Main() Dim builder As New StringBuilder("Initialize the StringBuilder.") builder.Replace("the", "my") Console.WriteLine(builder.ToString) End Sub End Module

Initialize my StringBuilder.

Replace, all instances. The Replace() Function does not just replace the first instance of a string it finds. It changes all of them, no matter how many there are.

Imports System.Text Module Module1 Sub Main() Dim builder As New StringBuilder("I see a cat, and the cat sees me.") ' Replace all instances of substring. builder.Replace("cat", "dog") Console.WriteLine("RESULT: {0}", builder) End Sub End Module

RESULT: I see a dog, and the dog sees me.

For-each. Here we use StringBuilder in a For-Each loop. Whenever we see Strings being appended in a loop, consider StringBuilder. It can improve runtime performance.

Here A String array is declared. It contains 3 strings. A new StringBuilder is instantiated with a certain value.

Detail In the For-Each loop, the Dim String is assigned to each String in the String array.

Finally The StringBuilder has each string (and a newline) appended to it. After the loop, the results are printed to the Console.

Console.WriteLine

Imports System.Text Module Module1 Sub Main() ' String array for use in loop. Dim items As String() = New String() {"Indus", "Danube", "Nile"} ' Initialize new StringBuilder. Dim builder As StringBuilder = New StringBuilder("These rivers are cool:").AppendLine ' Loop over each item in Array. For Each item As String In items builder.Append(item).AppendLine() Next ' Write result. Console.WriteLine(builder.ToString) End Sub End Module

These rivers are cool: Indus Danube Nile

Insert. This modifies a StringBuilder at the specified index. Here I specify the index 1, so the String literal is inserted after the first character in the buffer.

Imports System.Text Module Module1 Sub Main() Dim builder As StringBuilder = New StringBuilder("A cat") Console.WriteLine(builder) ' Insert this string at index 1. builder.Insert(1, " fluffy") Console.WriteLine(builder) End Sub End Module

A cat A fluffy cat

Remove. This erases characters from a StringBuilder and collapse those following it. In this example, I remove four chars starting at index 1.

Result The final data is missing those four chars, but contains the surrounding ones.

Imports System.Text Module Module1 Sub Main() Dim builder As StringBuilder = New StringBuilder("A big dog") Console.WriteLine(builder) ' Remove character starting at index 1. ' ... Remove 4 characters. builder.Remove(1, 4) Console.WriteLine(builder) End Sub End Module

A big dog A dog

Benchmark. In appending, StringBuilder is faster than String. Consider this benchmark: we want to append 3-character string (abc). We compare StringBuilder and String.

Version 1 This version of the code uses StringBuilder to append a string 100 times.

Version 2 Here we use String and its concatenation operator to append a string 100 times. This creates 100 strings.

Result When 2 strings are concatenated, a new String object results. Reducing allocations (with StringBuilder) improves performance.

Imports System.Text Module Module1 Sub Main() Dim m As Integer = 100000 ' Version 1: use StringBuilder. Dim s1 As Stopwatch = Stopwatch.StartNew For i As Integer = 0 To m - 1 Dim builder As StringBuilder = New StringBuilder For x As Integer = 0 To 99 builder.Append("abc") Next Next s1.Stop() ' Version 2: use String. Dim s2 As Stopwatch = Stopwatch.StartNew For i As Integer = 0 To m - 1 Dim str As String = "" For x As Integer = 0 To 99 str += "abc" Next Next s2.Stop() Dim u As Integer = 1000000 Console.WriteLine( s1.Elapsed.TotalMilliseconds.ToString("0.00 ms")) Console.WriteLine( s2.Elapsed.TotalMilliseconds.ToString("0.00 ms")) End Sub End Module

156.04 ms, StringBuilder Append 1020.00 ms, String concat

Performance advice. My research shows that appending two or three strings in a loop is faster than using StringBuilder. But using StringBuilder is faster for more than four iterations.

However It is best to almost always use StringBuilder in loops. It can avert a performance disaster in edge cases.

Dot Net Perls is a collection of tested code examples. Pages are continually updated to stay current, with code correctness a top priority.

Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.

This page was last updated on Jan 14, 2024 (edit link).

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